JP6853371B2 - Method for manufacturing silicone rubber composition for hydrogen gas seal - Google Patents

Description

The present invention relates to a method for producing a silicone rubber composition for hydrogen gas sealing. More specifically, the present invention relates to a method for producing a silicone rubber composition for hydrogen gas sealing, which has excellent kneadability / moldability, gas permeability (gas shielding property), and compression set resistance.

The Applicant first made the dimethylsiloxane copolymer unit a main component, and added 3 to 30 mol% of the methylphenylsiloxane copolymer unit or 5 to 50 mol% of the methylphenylalkylsiloxane copolymer unit and the methylvinylsiloxane. We have proposed a silicone rubber composition containing 0.2 to 8 parts by weight of an organic peroxide per 100 parts by weight of a methylphenyl vinyl-based or methylphenyl alkyl vinyl-based silicone rubber copolymerized with a polymerization unit (Patent Document 1). 2, 2).

This silicone rubber composition has excellent low temperature characteristics and blister resistance, and therefore, for example, a sealing material for a storage tank for high-pressure hydrogen gas stored at 70 MPa, specifically, cross-linked molding of O-rings, packings, gaskets, oil seals, valves, etc. It is stated that it can be suitably used as a material.

Further, in these patent documents, 50 to 120 parts by weight of silica is blended as a reinforcing agent, 12 parts by weight or less of a silica blending surfactant is blended per 100 parts by weight of silica, and a silica blending interface is blended. It is described that the activator is hexamethyldisilazane and that 50% by weight or less of water is used with respect to the weight of the surfactant for silica compounding.

Further, Patent Document 3 describes a silicone rubber composition containing a fibrous carbon nanostructure containing silicone rubber and carbon nanotubes as a silicone rubber composition having both flexibility and conductivity at a high level. , It is described that the fibrous carbon nanotube structure obtained from the adsorption isotherm uses a t-plot showing an upward convex shape.

However, from the viewpoint of the object of the invention, this silicone rubber composition naturally does not contain any description regarding gas shielding property.

WO 2007/145313 A1 WO 2008/001625 A1 WO 2016/136275 A1

In Patent Documents 1 and 2, normal physical properties (hardness, tensile strength, elongation at break), low temperature characteristics (TR-10, Tg) and blister test (70 MPa H ₂ , presence or absence of blister generation for He gas) are described. Although measured, an object of the present invention is to provide a method for producing a silicone rubber composition for hydrogen gas sealing, which maintains such excellent performance of the silicone rubber composition and further improves gas shielding properties. There is.

When producing a silica-blended silicone rubber composition for hydrogen gas sealing containing 2 to 8 parts by weight of carbon nanotubes per 100 parts by weight of silicone rubber, the silicone rubber contains a dimethylsiloxane copolymerization unit as a main component and methyl. A methylphenylvinyl-based silicone rubber or a methylfluoroalkylvinyl-based silicone rubber obtained by copolymerizing a phenylsiloxane copolymerization unit or a methylfluoroalkylsiloxane copolymerization unit and a methylvinylsiloxane copolymerization unit is used, and silicone rubber, carbon nanotubes and silica are used. A method for producing a silicone rubber composition for hydrogen gas sealing, which comprises kneading with a kneader and an open roll.

The silicone rubber composition for gas sealing of the present invention in which a specific amount of carbon nanotubes is blended with a silicone rubber, preferably a silicone rubber containing a dimethylsiloxane copolymerization unit as a main component, has excellent pressure resistance, low temperature resistance, and blister resistance of the silicone rubber. Since the gas shielding property, especially the hydrogen gas shielding property, is further improved without impairing the properties, the sealing material of the storage tank of the storage high-pressure hydrogen gas, specifically, O-ring, packing, gasket, oil seal, valve, etc. Can be suitably used as a cross-linking molding material of. In addition to hydrogen gas, it is also used to improve the shielding properties of carbon dioxide and chlorofluorocarbons.

The silicone rubber preferably contains a dimethylsiloxane copolymerization unit as a main component, as described in Patent Documents 1 and 2, and contains 3 to 30 mol% of a methylphenylsiloxane copolymerization unit or 5 to 50 mol%. A methylphenylvinyl-based or methylfluoroalkylvinyl-based silicone rubber obtained by copolymerizing a methylphenylalkylsiloxane copolymerization unit and a methylvinylsiloxane copolymerization unit is used.

Methylphenylvinyl-based silicone rubber contains a dimethylsiloxane copolymerization unit as a main component, and a methylphenylsiloxane copolymerization unit (3 to 30 mol%, preferably 10 to 25 mol% of all copolymerization units) is copolymerized with this. In addition, a small amount (about 0.1 to 5 mol%, preferably about 0.5 to 3 mol% of the total copolymerized units) derived from methyl vinyl siloxane (CH ₂ = CH) (CH _{3) SiO copolymerized units and the like is crosslinked with this.} Silicone rubber containing a vinyl group as a sex group is used.

When the copolymerization amount of the methylphenylsiloxane copolymerization unit is within this range, the methylphenylvinyl-based silicone rubber has a glass transition temperature Tg of -80 to -90 ° C, and can be used at extremely low temperatures. No blister is observed even under sudden decompression. On the other hand, if the copolymerization amount of the methylphenylsiloxane copolymerization unit is out of this range, sufficient low temperature characteristics cannot be obtained.

Actually, commercially available Shinetsu silicone products KE138Y-U, Dow coating products DY32-379U, etc. can be used as they are.

Methylfluoroalkylvinyl-based silicone rubber contains a dimethylsiloxane copolymerization unit as a main component, and a methylfluoroalkylsiloxane copolymerization unit, for example, γ, γ, γ-trifluoropropylmethylsiloxane (CF ₃ CH ₂ CH ₂ ) ( CH ₃ ) SiO copolymerization unit (5 to 50 mol%, preferably 20 to 40 mol% of all copolymerization units) is copolymerized, and methyl vinyl siloxane (CH ₂ = CH) (CH ₃ ) SiO is further copolymerized. Silicone rubber containing a vinyl group as a crosslinkable group of a small amount (about 0.1 to 5 mol%, preferably about 0.5 to 3 mol% in all copolymerization units) derived from a polymerization unit or the like is used.

Within this range of the amount of copolymerization of the methylfluoroalkylsiloxane copolymerization unit, the methylfluoroalkylvinyl-based silicone rubber has a glass transition temperature Tg of -80 to -120 ° C, and can be used at extremely low temperatures. Moreover, no blister is observed even under sudden decompression. On the other hand, when the copolymerization amount of the methylfluoroalkylsiloxane copolymerization unit is out of this range, the glass transition temperature Tg is at most about -70 ° C, which does not necessarily enable use at extremely low temperatures. In some cases, the blister resistance is not sufficient.

As the silicone-based rubber having the copolymerization composition defined in this way, it can be used as a rubber compound in which high-purity silica is blended with these silicone rubbers, and in fact, the commercially available Shin-Etsu silicone product KE- 871C-U etc. can be used as it is. It is also used as a blended rubber with other rubbers as long as the object of the present invention is not impaired.

In addition to these, silicone rubber or the like containing a monophenylsiloxane or diphenylsiloxane copolymer unit as a main component and having a vinyl group introduced therein can also be used.

As the carbon nanotubes [CNT] to be blended in the silicone rubber, those produced by any of the arc discharge method, the laser discharge method, the chemical vapor deposition method and the like can be used, and the multi-walled carbon nanotubes and single-walled carbon nanotubes can be used. Carbon nanotubes, carbon nanofibers, and the like can also be used. However, CNTs are smaller in size than graphite, and increasing the filling amount of CNTs significantly deteriorates the fluidity of the material. Moreover, since it is more expensive than graphite, it is preferable to use it with a small filling amount.

In order to exhibit the effect of conductivity with a small amount of filling, the fiber diameter of CNT should be small, and a fiber diameter of about 500 nm or less, preferably about 100 nm or less, and more preferably about 50 nm or less is used. , The average fiber length is about 500 μm or less, preferably about 1 to 100 μm.

Carbon nanotubes are used in a proportion of about 2 to 8 parts by weight, preferably about 2 to 6 parts by weight, per 100 parts by weight of silicone rubber. If the blending ratio is smaller than this, the object of the present invention of improving the gas shielding property is not achieved, while if the blending ratio is higher than this, the kneadability and moldability are particularly deteriorated.

In addition to carbon nanotubes, silicone rubber compositions include carbon black, talc, clay, graphite, silicate, calcium silicate and other reinforcing agents or fillers, and stearic acid, which are generally used as rubber compounding agents. , Processing aids such as palmitic acid and paraffin wax, acid receiving agents such as zinc oxide, magnesium oxide and hydrotalcite, antiaging agents, plasticizing agents and the like are appropriately blended and used.

Silicone rubbers such as methylphenylvinyl-based silicone rubbers and methylfluoroalkylvinyl-based silicone rubbers are vulcanized (crosslinked) with organic peroxides. As the organic peroxide, any one that can be generally used for rubber can be used without particular limitation. For example, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-third Butyl peroxide, 3rd butyl cumyl peroxide, dicumyl peroxide, 1,1-di (3rd butyl peroxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di ( 3rd Butyl Peroxy) Hexene, 2,5-Dimethyl-2,5-Di (3rd Butyl Peroxy) Hexin-3,1,3-Di (3rd Butyl Peroxyisopropyl) benzene, 2,5-Dimethyl -2,5-di (benzoylperoxy) hexane, 3rd butylperoxybenzoate, 3rd butylperoxyisopropyl carbonate, n-butyl-4,4-di (3rd butylperoxy) valerate and the like are used.

These organic peroxides are used in a proportion of about 0.2 to 8 parts by weight, preferably about 1 to 5 parts by weight, per 100 parts by weight of silicone rubber. Sufficient cross-linking density cannot be obtained if the ratio is lower than this, while if it is used at a higher ratio, the cross-linked molded product cannot be obtained by foaming, or even if it is obtained, the rubber elasticity and elongation are reduced. Become.

Preparation of the silicone rubber composition is carried out by kneading using a intermix, kneader, kneader and an open roll such as a Banbury mixer, it vulcanization (crosslinking molding) is an injection molding machine, compression molding machine , Generally performed by heating at about 150 to 200 ° C for about 3 to 60 minutes using a vulcanization press, etc., and if necessary, heating at about 150 to 250 ° C for about 1 to 24 hours. Next vulcanization) is performed.

Next, the present invention will be described with respect to Examples.

Example 1
100 parts by weight of silica-blended dimethylsiloxane copolymer rubber
(Shinetsu Silicone Product KE-871C-U)
CNT (Nanocyl product MWCNT NC7000) 2 〃
2,5-Dimethyl-2,5-bis (3rd Butyl Peroxy) Hexane 1 〃
(Shinetsu Silicone Product C-8)
Each of the above components was kneaded with a kneader and an open roll, and the kneaded product was press-crosslinked at 170 ° C. for 10 minutes and oven-crosslinked at 200 ° C. for 4 hours.

The following items were measured or evaluated for the kneaded product and the crosslinked product.
Kneadability / moldability:
Cohesiveness, wrapping property, kneading of unvulcanized dough (kneaded product) at the time of kneading
Comprehensive sensory evaluation of time, etc., ○ based on good, △ slightly worse
, Evaluation of deterioration as × Gas permeation test:
JIS K 7126-1: 2006 plastics that comply with ISO 15105-1
Lum and sheet-Plate-shaped addition with a thickness of 1 mm according to the gas permeability test
Hydrogen gas permeability coefficient (unit: H ₂ /30℃/0.6MPa) For vulcanized sheets measuring the
Determined, using Comparative Example 1 as a reference (1.00), and a hydrogen gas permeation charge for this.
Calculated ratio of numbers (referenced gas permeability coefficient) Compressed set:
JIS K-6262: 2013 vulcanized rubber and thermoplastics conforming to ISO 815-1
Rubber-Similar to how to obtain compression set at room temperature, high temperature and low temperature
Therefore, for the O-ring-shaped crosslinked product, after 1000 hours at 150 ° C.
Measure the compression set value of

Example 2
In Example 1, the amount of CNT was changed to 3 parts by weight.

Example 3
In Example 1, the amount of CNT was changed to 5 parts by weight.

Example 4
In Example 1, the amount of CNT was changed to 7 parts by weight.

Comparative Example 1
In Example 1, CNT was not used.

Comparative Example 2
In Example 1, the amount of CNT was changed to 1 part by weight.

Comparative Example 3
In Example 1, the amount of CNT was changed to 10 parts by weight.

Comparative Example 4
In Example 1, instead of 2 parts by weight of CNT, 5 parts by weight of flat talc (Imeris Specialties Japan product Mistron Vapor, average particle size of about 6.1 μm) was used.

Comparative Example 5
In Example 1, 20 parts by weight of flat talc (Mistron Vapor) was used instead of 2 parts by weight of CNT.

The results obtained in each of the above Examples and Comparative Examples are shown in the following table.

table
Example Kneadability / formability Standardized gas permeability coefficient Compressive set strain (%)
Example 1 ○ 0.97 41
〃 2 ○ 0.94 43
〃 3 ○ 0.90 45
〃 4 ○ ~ △ 0.82 49
Comparative Example 1 ○ 1.00 31
〃 2 ○ 1.00 39
〃 3 △ ~ × 0.75 60
〃 4 ○ 0.98 35
〃 5 △ 0.95 72

From the above results, the following can be said.
(1) In each example, the standardized gas permeability coefficient is 0.97 or less, although the compression set is deteriorated.
(2) However, in Example 4 in which 7 parts by weight of CNT was used, a slight decrease in kneadability and moldability was observed.
(3) In Comparative Example 3 in which 10 parts by weight of CNT was used, the kneadability / moldability and the compression set were significantly deteriorated.
(4) In Comparative Example 4 (5 parts by weight) using the flat filler (talc), almost no effect of improving the hydrogen gas shielding property was observed, and in Comparative Example 5 (20 parts by weight), some hydrogen gas shielding was observed. Although the effect of improving the property was observed, the kneadability and moldability were slightly lowered, and the compression set was greatly deteriorated, and there was a problem in the sealing property.

Claims (7)

When producing a silica-blended silicone rubber composition for hydrogen gas sealing containing 2 to 8 parts by weight of carbon nanotubes per 100 parts by weight of silicone rubber, the silicone rubber contains a dimethylsiloxane copolymerization unit as a main component and methyl. A methylphenylvinyl-based silicone rubber or a methylfluoroalkylvinyl-based silicone rubber obtained by copolymerizing a phenylsiloxane copolymerization unit or a methylfluoroalkylsiloxane copolymerization unit and a methylvinylsiloxane copolymerization unit is used, and silicone rubber, carbon nanotubes and silica are used. A method for producing a silicone rubber composition for hydrogen gas sealing, which comprises kneading with a kneader and an open roll.
The method for producing a silicone rubber composition for hydrogen gas sealing according to claim 1, which does not contain a surfactant for blending silica and water. The method for producing a silicone rubber composition for hydrogen gas sealing according to claim 1, wherein 2 to 6 parts by weight of carbon nanotubes are used. The method for producing a silicone rubber composition for hydrogen gas sealing according to claim 1, wherein carbon nanotubes having a fiber diameter of 500 nm or less and an average fiber length of 500 μm are used. The method for producing a silicone rubber composition for a peroxide crosslinkable hydrogen gas seal according to claim 1, further comprising an organic peroxide. A hydrogen gas sealing material obtained by cross-linking a silicone rubber composition for a peroxide crosslinkable hydrogen gas seal produced by the method according to claim 5. The hydrogen gas sealing material according to claim 6, wherein the ratio of the hydrogen gas permeability coefficient to the hydrogen gas permeability coefficient when the hydrogen gas permeability coefficient is 1.00 when the carbon nanotubes are not blended is 0.97 or less.